The present invention pertains to an electrical circuit, and particularly one for use in providing a time-related voltage when power is disconnected from an electrical system.
Most machinery or equipment is required to be de-energized for at least brief periods of time. In the field of gas turbine engines used for aircraft, for example, the downtime is a significant factor in the amount of thermal cyclic fatigue inasmuch as cooling and thermal creep take place during the downtime and engine wear is directly related, therefore, to the time period in which the engine is turned off.
As is well known, aircraft main battery supplies are typically meager and individual equipment batteries highly undesirable. Therefore, with the engine off and no charging current available, the electrical system of the aircraft is typically turned off. Thus, when the aircraft is parked and the engine is turned off, the instruments will also be depowered, thereby preventing the utilization of a powered clock for providing downtime information to an engine life monitor such as that disclosed in U.S. Pat. No. 4,580,127, filed Mar. 28, 1983 and entitled CIRCUIT FOR CONVERTING ANALOG BIPOLAR SIGNALS TO DIGITAL SIGNALS.
There exists, therefore, a need for a system for measuring the downtime of an engine without available power and supplying such information to an engine life monitor circuit when the instrumentation and the aircraft power is re-energized. Thus it is desirable to provide an interval timer which provides timing information independently of the aircraft's power system when power is unavailable and which information can be sampled once power is again restored.